Homebrew PCBs

Stefan Trethan wrote:
> On Mon, 27 Jun 2005 18:11:47 +0200, Leon Heller  
> <leon.heller@...> wrote:
> 
> 
>>If it's only for occasional use, why not pump up an old car wheel and  
>>tyre.
>>That should have plenty of pressure and capacity to etch a few boards.  
>>Can't
>>be a closed system, of course.
>>Leon
> 
> 
> 
> closed system is main requirement or i would use shop air. I'm not  
> spreading any more etchant mist than needed.
> 
> thanks
> 
> ST
> 

I've never notice actual mist from bubbling etchant. However, if your 
trying to minimize gaseous fumes then a sealed system is the only 
option. Bubbles do create a lot of splashes and fine droplets that will 
travel a surprising long distance. If you can sufficiently cover the 
etchant so that droplets run back in to the tank, then that should solve 
most of your problems. My spray etcher does creates a heck of lot of 
mist and it is not "closed loop". There is an air bubbler in the spray 
chamber for aerating the etchant and I get virtually no etchant escaping 
even though the "air" is continuously escaping. By far most etchant 
escapes from spillage as I withdraw the PCB. The trick was to install a 
double walled opening. The theory is that mist will immediately settle 
upon contact with a surface. So you all you have to do it make sure the 
mist is very likely to contact a surface.

Now you won't be limited to corrosion resistant air pumps. And even 
aquarium pumps don't like acid. They usually have a zinc screw 
connecting the diaphragm to the oscillating arm, and I've found the 
valve flap material breaks down too. I can guarantee you'll get more 
problems then you'll solve trying to recirculate the etchant chamber gases.

Adam